Dipping mandrel with a gap

ABSTRACT

A mandrel for molding polymer valve leaflets for heart valve prostheses is disclosed, including a body portion including an outer surface with ridges and contoured surfaces corresponding to the leaflets, the upper edge of the contoured surfaces corresponding to the free upper edge of the leaflets, and the mandrel including a mandrel extension above the body portion, and a gap extending around the mandrel between the upper edge of the contoured surface and the mandrel extension. A process for producing these polymer valve leaflets is also disclosed by dip coating with this mandrel and removing the polymer film created at the gap, preferably by applying suction or blowing thereto.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/235,560, filed Jan. 28, 2014, which is a national phase entryunder 35 U.S.C. § 371 of International Application No. PCT/US2012/047293filed Jul. 19, 2012, published in English, which claims the benefit ofthe filing date of U.S. Provisional Patent Application No. 61/512,999filed Jul. 29, 2011, the disclosures of which are all herebyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods for forming polymer valveleaflets for prostheses. More particularly, the present inventionrelates to methods for forming such valve leaflets by dip coating onto amandrel. The present invention also relates to a mandrel for the dipcoating of polymer leaflets for forming valve prostheses.

BACKGROUND OF THE INVENTION

Prosthetic heart valves with flexible leaflets, including thosesupported by a stent structure, are well known in the art. A variety ofsuch prostheses are known for correcting problems associated with thecardiovascular system and in particular the heart. Therefore, theability to replace or repair diseased heart valves with prostheticdevices has become a well-used method for treating heart valvedeficiencies due to disease and congenital defects.

Prosthetic heart valve leaflets thus perform the function of opening andclosing to regulate blood flow through the valve. These heart valveleaflets must therefore typically either pivot or flex with each cycleof the heart to open and close. The prostheses themselves have beenconstructed from natural materials such as tissues, synthetic materials,or combinations thereof. Prostheses formed from purely syntheticmaterials can, for example, be manufactured from biocompatible metals,ceramics, carbon materials, and polymers. In these cases, the leafletscan be either rigid or flexible in various embodiments.

Those heart valve prostheses which include flexible leaflets can be madefrom tissue leaflets or polymer leaflets. The use of polymer leafletshas become more desirable, particularly in accordance with the searchfor durable and stable leaflet performance over a number of years ofuse.

According to U.S. Pat. No. 6,953,332 (“the '332 Patent”) and U.S. Pat.No. 7,682,389 (“the '389 Patent”), dip coating methods and mandrels areused to form these polymer leaflets and valve prostheses. Such a mandrelis shown, for example FIG. 1 hereof, which corresponds to FIG. 8 of the'332 Patent, including an upper surface 314 and a number of contours 310which correspond to the number of valve leaflets desired. The dipcoating process disclosed in the '332 and '389 Patents is one in whichthe mandrel itself defines the leaflet profile or shape, and after thedipping process takes place, it is generally necessary to then conduct atrimming step in order to cut the extra polymer off along the free edgeof the leaflet on the mandrel (see FIG. 7). This step, in turn, requiresa precisely controlled apparatus with a cutting instrument applied tothe leaflet and the mandrel. This, in turn, can cause defects on theleaflet at that cutting edge and on the mandrel as well, requiringprecisely machined and polished mandrel surfaces which therefore must beabandoned after the trimming step. Indeed, this also restricts the typeof materials which can be used for the mandrel itself, since mandrelsmade of certain materials such as stainless steel would not be suitableto be applied to particular cutting instruments used thereon.

These leaflets can also be dip-coated inside an associated collapsiblestent, such as those in use in connection with trans-catheter aorticvalve implantation (see FIG. 6). In this case, the trimming processbecomes even more difficult, particularly where the leaflet is insidethe cage-like stent, as shown in FIG. 6. Since in the currently usedprocess the leaflet cannot be trimmed inside the strut-surrounded stent,the leaflet must be preformed, trimmed, and then removed from themandrel, and then bonded to the stent with an additional step beforeboth the polymer of the leaflet and the polymer coated on the stent arefully cured. This therefore results in a weaker bonding force betweenthe leaflet and the stent which cannot satisfy the functionalrequirements of the valve and which provide for a much more complicatedmanufacturing process.

The search has therefore continued for a better manufacturing processfor polymer stents, particularly in connection with the mandrel dippingprocess, and for potential trimming processes within the stent.

SUMMARY OF THE INVENTION

In accordance with the present invention, this and other objects havenot been realized by the discovery of a method for providing at leastone polymer valve leaflet for a prosthesis comprising providing amandrel including an outer surface having a plurality of ridges and atleast one contoured surface between the plurality of ridges, whereby theat least one contoured surface corresponds to at least one leaflet forthe prosthesis, the at least one contoured surface including an upperedge portion corresponding to the upper free edge of the at least oneleaflet, the mandrel further including a mandrel extension portion abovethe upper edge portion including a top surface, and a circumferentialgap extending around the mandrel between the upper edge portion of theat least one contoured surface and the mandrel extension portion,dipping the mandrel into a preselected polymer solution for providingthe at least one leaflet, removing the mandrel from the predeterminedpolymer solution, removing the predetermined polymer solution from thearea of the circumferential gap, curing the polymer to provide the atleast one polymer valve leaflet, and removing the at least one polymervalve leaflet from the mandrel. In a preferred embodiment, the removingof the predetermined polymer solution comprises providing suction or apartial vacuum to the area of the circumferential gap, or in anotherembodiment applying a stream of gas to the area of the gap. Preferably,the gas comprises nitrogen or air.

In accordance with one embodiment of the method of the presentinvention, the at least one contoured surface comprises three contouredsurfaces, and the at least one leaflet comprises three leaflets for theprosthesis.

In accordance with another embodiment of the method of the presentinvention, the step of removing the predetermined polymer solution fromthe area of the circumferential gap comprises moving a vacuum tip or agas pressure tip circumferentially around the gap.

In accordance with another embodiment of the method of the presentinvention, the predetermined polymer solution comprises a syntheticpolymer or a purified biological polymer. Preferably the syntheticpolymer is a flexible polymer material such as polyurethane,polyurethane-silicone copolymer, poly(styrene-b-isobutylene-b-styrene),polydimethyl siloxanes, polytetrafluroethylene, and derivatives andmixtures thereof.

In accordance with another embodiment of the method of the presentinvention, the polymer solution includes a solvent, and the polymersolution is solidified by evaporating the solvent. Preferably, dippingof the mandrel into the preselected polymer solution comprises aplurality of dipping steps.

In accordance with the present invention, a mandrel has been discoveredfor the molding of a polymer valve leaflet for a prosthesis, the mandrelcomprising a body portion including an upper surface having a pluralityof ridges, and at least one contoured surface between the plurality ofridges, whereby the at least one contoured surface corresponds to atleast one leaflet for the prosthesis, the at least one contoured surfaceincluding an upper edge portion corresponding to the upper free edge ofthe at least one leaflet, the mandrel further comprising a mandrelextension portion disposed above the body portion, and an intermediatecircumferential gap extending around the mandrel between the upper edgeportion of the at least one contoured surface and the mandrel extensionportion. In a preferred embodiment, the circumferential gap includes agap having a depth of between about 1 and 5 mm, and preferably betweenabout 1 and 2 mm.

In accordance with another embodiment of the mandrel of the presentinvention, the at least one contoured surface comprises three contouredsurfaces, and the corresponding at least one leaflet comprises threeleaflets.

In accordance with another embodiment of the mandrel of the presentinvention, the body portion comprises a cylindrical body portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully appreciated with reference tothe following detailed description which, in turn, refers to thedrawings in which:

FIG. 1 is a side, elevational view of a dipping mandrel in accordancewith the prior art;

FIG. 2 is a side, perspective view of a heart valve prosthesis with theleaflets in a relaxed state, in which the valve is approximately fullyopen, as in the prior art;

FIG. 3 is a side, perspective view of a dipping mandrel in accordancewith the present invention;

FIG. 4 is a front, elevational view of the dipping mandrel shown in FIG.3;

FIG. 5 is a top, elevational view of the dipping mandrel shown in FIG.3;

FIG. 6 is a side, perspective view of an aortic valve prosthesis with acollapsible stent, as in the prior art; and

FIG. 7 is a side, perspective view of a valve prosthesis with leafletsin accordance with the prior art, in which extra polymer needs to betrimmed off.

DETAILED DESCRIPTION

The dip coating process of the present invention utilizes an improvedmandrel design which has now been developed in order to facilitate theproduction of polymer leaflets for heart valve prostheses. The improvedmandrel design in this case employs a mandrel in which a mandrelextension is provided above the upper edge of the surface of the mandrelcorresponding to the free edge of the leaflets, and includes a gapbetween that free edge of the leaflets and the top surface of themandrel extension.

In this manner, instead of the need to trim the upper surface of themandrel, such as that shown in FIG. 1, or to trim extra polymer, such asshown in FIG. 7, with all of its concomitant difficulties, it is nowpossible to entirely eliminate such a trimming step. This isaccomplished by removing polymer from the area of the gap between thelower edge of the gap corresponding to the free edge of the leaflets andthe upper edge of the gap. This is facilitated by the fact that, in viewof surface tension created during the dipping process, while the outersurface of the gap includes a film of the polymer, the inner surface ofthe gap is essentially free of polymer. It is thus possible to removethis polymer film using a vacuum, or a stream of air or other gas, in avery simple process. This, in turn, not only provides for smootherleaflets being formed, but simplifies the overall process for doing so.

The improved polymer leaflets of the present invention can then be usedfor the very same purposes for which they have been produced and used inthe past. They can thus be used to form valve prostheses, andparticularly heart valve prostheses. Damaged or diseased natural heartvalves can thus be replaced with these valve prostheses in order torestore valve function. The use of polymer-formed flexible leaflets thusmimics the action of natural tissue leaflets but permits replacement ofheart valves, including aortic, mitral, tricuspid, or pulmonary valves.

The leaflets of the present invention can also be used with a supportstructure, such as an ordinary stent (FIG. 2) or a collapsible stent(FIG. 6). The rigid support or stent thus provides a support structurefor the leaflets, and generally includes commissure supports for theends of the free edge of the leaflets and scallops/stents supporting theattached edges of the leaflets extending between the commissure supportsthemselves. In a preferred embodiment, the outer diameter of the mandrelis tightly mated with the inner diameter of the stent, and they are thendip-coated together. In this manner, the polymer leaflets will firmlybond with the stent.

The leaflets of the present invention are thus formed from a thin filmof flexible polymer. Suitable polymers are biocompatible, in that theyare nontoxic, noncarcinogenic, and do not induce hemolysis or animmunological response. Heart valve prostheses formed from polymers arepreferably non-thrombogenic, and relevant mechanical properties of thesepolymers can include, for example, stiffness, strength, creep, hardness,fatigue resistance and tear resistance. The preferred polymers for usein accordance with the present invention are durable in that they do notsignificantly lose their flexibility or their mechanical strengthfollowing years of use.

The preferred process for preparing polymer leaflets is by a dip coatingmethod using a mandrel. Thus, the mandrel surface is contoured toconform to leaflets, and a thin polymer layer is applied to the mandrel,generally by a dip coating process. The leaflets can then be removedfrom the mandrel in a relaxed state corresponding to a nearly closedleaflet configuration, a fully open configuration, or a partially openleaflet configuration. In any event, the leaflet shape along with itsfree edge is defined by the profile below the gap, and the polymer whichcovers the mandrel extension above the gap is discarded.

The valves include a plurality of leaflets, preferably three leaflets.They are supported by a support structure for use in either open heartsurgery or trans-catheter valves.

A typical heart valve prosthesis with the leaflets in a relaxed state inan almost fully open position is shown in FIG. 2. This heart valveprosthesis 1 includes leaflets (2, 4 and 6), commissure supports (8, 10and 12), support structure/stent (14) and sewing ring (16). The supportstructure/stent (14) can be relatively rigid, such that the supportstructure functions as a stent to maintain leaflet function withattachment to the patient at the base (18) of support structure (14).Alternatively, support structure (8) can be less rigid as part of astentless valve, with support structure (8) being secured to otheranatomical structures or other devices to maintain the leaflet function.

The support structure includes commissure supports (8, 10 and 12) andscallops (20, 22 and 24) between the commissure supports. Free edges(30, 34 and 42) of leaflets (2, 4 and 6, respectively) join at thecommissure supports (10, 12 and 14). Attached edges (34, 36 and 38) ofleaflets (2, 4 and 6) also attach to the support structure alongscallops (20, 22 and 24). If the support structure (14) is not rigid, itshould be secured to anatomical structures of other devices to maintainleaflet function.

In the case of a trans-catheter valve 100, as shown in FIG. 6, thesupport structure is a collapsible stent with struts 102. These struts102 form cells 104 which thus allow the stent to be collapsed, so thatit can be loaded into a catheter. The stent 100 can be self-expandableor it can be expanded by means of a balloon to be deployed in thediseased valve location in order to replace the function of the diseasedvalve. Once deployed, the expanding radial force generated by theself-expandable stent at its smaller diameter, as compared to itsnatural diameter, anchors the valve to the surrounding tissue. Theballoon expandable stent is expanded by the balloon, and thus anchors tothe surrounding tissue by this expanding force.

The sewing ring (16) generally extends from base (18) of the supportstructure (14) and facilitates attachment of the heart valve prosthesisto the patient or other components of a device. Sutures, staples, orother fastening mechanisms can be passed through the sewing cuff tosecure it to the patient's tissue annulus, etc. In general, atrans-catheter valve does not require a sewing ring.

Turning to FIG. 3, the improved mandrel of the present invention isshown therein. The mandrel itself (50) has a generally unitary andpreferably cylindrical configuration. The mandrel (50) includes a lowershaft portion (52) leading up to the contoured portion (54). The lowershaft portion (52) is generally used to grip the mandrel (50) during thedip coating process itself. The lower shaft portion (52), whilepreferably cylindrical, can have other shapes and/or structural featuressuch as appendages, holes or cavities to facilitate the grippingprocess. Generally, the cylindrical shaft portion (52) can be connectedto an automated apparatus to lower the mandrel in a reproducible mannerinto the polymer coating material during the dip coating process.

The central contoured portion (54) is configured to produce structureswith appropriate shapes to generate desired features in the polymerwhich is cast onto the mandrel surface. Above the contoured portion (54)is the dipping mandrel extension (56). This portion terminates in topsurface (58) thereof. The central contoured portion (54) includes aplurality of ridges (60) which correspond to the commissure supports ofthe valve itself. Scalloped portions (62) connect between the ridges(60) and correspond with scallops extending between the commissuresupports in the support structure. Thus, contoured surfaces (64) areformed between the ridges (60) and the scallops (62). The leaflets arethus formed on these contours (64). The attached edge of the leafletsfollows the commissure support and scallops of the valve, whichcorresponds to ridges (60) and scallops (62) on the mandrel (50).

Above the lower shaft portion (52) and below the upper mandrel extension(56) is located a gap or groove (68). This gap (68) extendscircumferentially around the entire mandrel (50) defining a separationbetween the upper end of the contoured portion (54) of the mandrel (50)and the lower end of the mandrel extension portion (56). The gap (68)itself thus includes a lower surface (70), an upper surface (72) and aninner indented vertical surface (74). The width of the gap (68) thuscomprises a distance between the lower surface (70) and the uppersurface (72), and will generally be between 0.5 and 5 mm, preferablyabout 1 mm. The depth of the gap (68), that is the distance from theouter surface of the mandrel (50) and the vertical wall (74) will alsobe between about 1 and 5 mm, preferably about 1 mm.

The edge (80) of the lower surface (70) of the gap (68) thus forms aboundary between the contours (64) and the lower surface (70) of the gap(68).

The ridges (60) thus mark the end point of the free edges of theleaflets and the separation between adjacent leaflets. These ridges (60)have various shapes to correspond to the desired valve performancecharacteristics. In addition, a support structure or stent can beattached to the mandrel along these ridges (60) prior to the dip coatingtaking place. If the polymer structure is attached to a supportstructure following removal from the mandrel, polymer along the ridgesis associated with at least a portion of the commissure supportseparating adjacent leaflets. Ridges (60) help to provide propercoaptation of the closed leaflets.

The contours (64) themselves are machined (including injection molded,cast, etc.) in order to provide the desired shape for the leaflets to beultimately produced, in their relaxed position. The leaflets have ashape approximating their fully open position. However, the leaflets canbe formed in a relaxed configuration corresponding to partially closedvalve positions.

In order to form the polymer leaflets, the mandrel of the presentinvention is preferably dip coated into a liquid polymer solution inorder to cast the polymer onto the mandrel surface. The polymer issolidified on the surface of the mandrel to form a polymer structure.

Therefore, in the course of the dipping process itself, a thin film ofpolymer will be formed over the gap (68), and in view of surface tensionformed thereon upon removal of the mandrel from the polymer solution,will not enter into the gap and/or reach the inner wall (74) thereof.Thus, in a separate process step, the removal of this thin layer or filmof polymer overlying the gap (68) will eliminate the aforementionedtrimming process, and result in an upper leaflet edge (a free edge)which is smooth, clear and well defined.

The step of removal of the polymer from the area of the gap (68) cancomprise the application of a stream of gas such as air or nitrogen, orthe application of a vacuum to remove the polymer film. This can be doneby means of a pipette or with a vacuum tip before the polymer solutionis fully cured. The timing which is employed in order to remove thepolymer solution will depend upon the physical properties of thepolymer, such as its viscosity and surface tension, so that the polymerwhich covers the gap can be sucked into a pipette or vacuum tip or blownout of the gap, while the polymer on the body portion of the mandrelwill not continuously flow across the gap. Care must be taken so as notto damage the coated polymer on the body portion of the mandrel, such asby adjusting the strength of the vacuum applied or the pressure of thegas stream applied thereto. The thin layer of polymer which covers thegap can be removed manually using a pipette or vacuum tip or a gasstream. This thin polymer layer can also be removed automatically by theuse of a robotic arm holding a vacuum tip or a gas pressure tip. Thus,one robotic arm can move circumferentially along the mandrel gap inorder to remove the thin layer of polymer completely around the mandrel.On the other hand, a number of robotic arms, such as two or three, cansimultaneously remove the thin layer of polymer in each of the leaflets(e.g., one for each leaflet in the case of three such arms).

Suitable polymeric materials for formation into the leaflets include,for example, synthetic polymers as well as purified biological polymersand combinations thereof. Flexible polymers include elastomers and otherpolymers that can sustain significant flexure, bending, twisting, wearand/or deformation without structural failure. Appropriate syntheticpolymers include, without limitation, polyamides (e.g., nylon),polyesters, polyacrylates, vinyl polymers (e.g., polyolefins,polyethylene, polytetrafluoroethylene or other halogenated polymers,polypropylene, ethylene-propylene copolymers, ethylene-propylene-dienemonomer copolymer (EPDM) and polyvinylchloride), polycarbonates,polyacetals (e.g., Delrin®), polyurethanes, polyurethane-siliconecopolymers, poly(styrene-b-isobutylene-b-styrene), polydimethylsiloxanes, cellulose acetates, ethylene vinyl acetates, polysulfones,nitrocelluloses, derivatives thereof, similar copolymers, and mixturesthereof. Particularly preferred flexible polymer materials for theformation of flexible polymer heart valve leaflets include, for example,polyurethanes, polyurethane-silicone copolymers,poly(styrene-b-isobutylene-b-styrene), polydimethyl siloxanes,polytetrafluoroethylenes, derivatives thereof and mixtures thereof.

Biological polymers can be naturally occurring or produced in vitro by,for example, fermentation and the like. Purified biological polymers canbe appropriately formed into a substrate by techniques such as weaving,knitting, casting, molding, extrusion, cellular alignment and magneticalignment. Suitable biological polymers include, without limitation,collagen, elastin, silk, keratin, gelatin, polyamino acids,polysaccharides (e.g., cellulose and starch) and copolymers thereof.

Preferred polymers are biocompatible. In preferred embodiments offlexible leaflets, the polymer leaflets generally have a thickness fromabout 50 microns to about 1000 microns and more preferably from about100 microns to about 300 microns. A flexible polymer used to form theleaflets of heart valve prostheses is preferably a polymer that hassufficient durability to withstand the repeated cycling required forreplacement heart valve use. For a human patient, the valve must cycleabout 40 million times each year, and the valve ideally remainsfunctional over the remaining natural expected lifetime of the patient.Current tissue valves may require replacement following about 400million to about 600 million cycles. Therefore, the polymer substratepreferably can withstand at least about 400 million cycles and morepreferably can withstand more than about 600 million cycles withoutsignificant structural deterioration. Polyurethanes and siliconepolymers are particularly preferred for achieving these performancerequirements.

The polymer leaflets flex between a generally fully open position and agenerally closed position. In the open position, the free edges of thepolymer leaflets form the downstream opening of the valve and do notsignificantly resist forward blood flow. In the closed position, thefree edges of adjacent leaflets contact in the coaptation region toclose the valve and do not allow significant leakage. While the leafletsflex between the open position and the closed position in use, theleaflets have a natural relaxed position when no forces are applied.When the leaflets are formed on a mandrel, the shape of the mandrelcorresponds to the relaxed position of the leaflets since the polymerforms on the mandrel from a liquid without the application of anystresses to the polymer. By adjusting the shape of the mandrel, therelaxed position of the leaflets can be selected to have a desiredshape.

In particular, the relaxed state of the leaflets corresponding to themandrel shape can approximate a fully open position of the valve suchthat the polymer material is under little, if any, stress in the fullyopen position. Alternatively, the leaflets can have a relaxed positioncorresponding to an almost closed valve. In other alternativeembodiments, the leaflets can have a relaxed position intermediatebetween the open position and the closed position. The processing of thevalves to form the prosthesis is similar regardless of the relaxedconfiguration of the leaflet, except for the machining of the mandrel toproduce the desired relaxed position of the leaflets.

The polymer leaflets can include one or more reinforcements tostrengthen the leaflets. The reinforcement can be formed as a thickeningof the flexible polymer or as an additional composition bonded to theflexible polymer forming the body of the leaflet, with or withoutthickening of the leaflets themselves. The reinforcement can belocalized or can extend over a significant portion of the leaflet area.

As for the polymer liquid itself which is used to perform the dipcoating process, these polymer solutions or dispersions comprise theabove polymers dissolved or dispersed in a solvent. The solvent can beselected based on the particular polymer used. Thus, for polyurethanes,suitable solvents generally include, for example, N,N-dimethylacetamideand tetrahydrafuran. The solution concentration can be selected to yieldan appropriate viscosity and coating thickness. The coating thicknesswill generally depend on the concentration or viscosity of the polymersolution. Desirable polymer concentration (i.e., solid content) willgenerally range from about 1 wt. % to about 50 wt. %, and morepreferably from about 8 wt. % to about 30 wt. %.

To perform the dip coating process the mandrel is connected to aninstrument that lowers the mandrel a predetermined depth into thepolymer liquid. The mandrel preferably is dipped slowly into thesolution to avoid significant disruption of the solution. Speed ofinsertion and withdrawal can also effect the coating thickness, withfaster dipping resulting in a thinner polymer layer. In particular, forforming an initial polymer layer if multiple layers are applied, thefirst dip would preferably be slow. Actual values of dipping velocitywill depend on the properties of the polymer solution.

The position of the lower edge along the base of the polymer valvestructure is determined by the depth that the mandrel is inserted intothe polymer liquid. If the depth of the insertion of the mandrel intothe polymer liquid is controlled within a desired range, the lower edgeof the polymer valve structure has a position within desired toleranceswithout cutting the lower edge of the structure. Generally, the mandrelis dipped at least to a position corresponding to the location at whicha sewing cuff is added. However, the mandrel can be dipped to a greaterdepth. The dip coating can be performed manually by hand or with amechanical device similar to a drill press to lower the mandrel by themanual rotation/movement of a lever. Alternatively, a motorized linearactuator or robot could be used to lower the mandrel into the solution.Automated dipping provides for greater control of the speed andresolution for more consistency between polymer structures.Alternatively, the mandrel and/or stent assembly can be placed inside achamber to be filled by the polymer solution. The polymer solution canthen be drained from the chamber, leaving only the coated polymersolution on the mandrel and/or stent.

Polymer coatings from polymer solutions are solidified by evaporatingthe solvent to leave behind the polymer. The solvent can be removed byexposure of the coated mandrel to the ambient atmosphere or, preferably,in an accelerated process by heating the coated mandrel. The coatedmandrel can be heated in an oven or the like. Similarly, polymer meltscoated onto a mandrel are solidified by cooling the polymer. Again, thecooling can be performed by exposing the polymer coated mandrel to theambient atmosphere or under accelerated conditions by further coolingthe coated mandrel in a refrigerator or the like.

As noted above, optional reinforcements can be placed within the polymerstructure to reinforce the polymer, especially near the edge. Thereinforcement material can be placed along the mandrel prior to thecoating process. Alternatively, the reinforcement material can be placedover a layer of polymer after it is coated onto the mandrel. Thereinforcement can be placed over the polymer prior to completesolidification or following solidification. A further polymer layer canbe placed on the mandrel following placement of a reinforcing materialover a polymer coat.

More than one polymer coating can be applied by dip coating in order toobtain a thicker polymer structure. Additional layers can be made usingthe same polymer liquid or a different polymer liquid. In particular,the polymer composition can be the same or different in a plurality ofpolymer liquids for dip coating. Different polymer compositions can bedifferent with respect to chemical composition, molecular weightdifferences, concentrations, solvents or other features of thecompositions.

Following application of all polymer coats and solidification of thepolymer(s) on the mandrel, the polymer structure is separated from themandrel. Before this takes place, however, the polymer film producedacross the gap 68 must be removed. This is readily accomplished, asdiscussed above, by use of a vacuum or a flow of gas, such as air, ornitrogen, to remove that film before it fully cures. This is not only asimple operation, but it is one that thereby entirely eliminates theneed for the far more complex trimming operation required in the past,as with the mandrel shown in FIG. 1.

In preferred embodiments the cured polymer is separated into two partson the mandrel by means of the gap; the upper part covers the mandrelextension and the lower part covers the central contoured portion (54)and its associated stent. The upper part of the polymer can be removed,such as by tweezers or the like, and discarded. The lower part of thepolymer, preferably along with its associated stent, can be carefullyslid off of the mandrel, preferably in a liquid such as hot water, alsopreferably with the help of tweezers or the like, without damaging thepolymer.

Generally, the polymer, preferably along with its associated stent, isremoved from the mandrel manually. After removal from the mandrel, thepolymer leaflet(s) 10 are firmly bonded with its associated stent, andan integrated valve prosthesis is thus formed. Alternatively, if thestent is not associated during the dip-coating process, the polymervalve structure separated from the mandrel can be processed into acomplete prosthesis. If desired, the polymer valve structure can bestored prior to completing the prosthesis, preferably under conditionswere the leaflet structures are not damaged.

Formation of Prostheses

After the leaflets are formed, additional processing steps may be neededin order to complete production of the prosthesis. In preferredembodiments, the support structure/stent is formed in association withthe polymer structure during the dip coating process. In alternativeembodiments in which the leaflets were not formed directly inassociation with a support structure/stent or if an additional supportstructure is desired, the polymer valve structure is connected to thesupport structure using, for example, a mechanical fastener, suture oradhesive. Any additional structures, such as a sewing cuff, areconnected to the support structure. Sewing cuffs and the like generallyare added at or near the inflow edge.

If the valve is incorporated into a conduit, the conduit can beconnected to or formed around the valve such that the valve is securelyconnected to the conduit. Similarly, the valves can be secured within aconduit prior to attaching the conduit to remaining portions of a leftventricular assist device. Suture, staples, adhesive, and otherfastening mechanisms and combinations thereof can be used to connect thesupport structures to the other components.

Packaging, Distribution and Use

For distribution, the medical devices are placed in sealed and sterilecontainers. The valves can be placed in a holder that supports the baseof the valve without damaging the polymer leaflets. The containers canbe dated such that the date reflects the maximum advisable storage time,if components of the medical device should not be stored indefinitely.The containers are packaged along with instructions for the proper useand/or implantation of the medical device and along with otherappropriate and/or required labeling. The containers are distributed tohealth care professionals for use in appropriate medical procedures,such as implantation of a prosthesis and the like. Heart valveprostheses and valved vascular prostheses can be implanted, for example,using standard surgical procedures or trans-catheter apparatus.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A mandrel for the molding of at least onepolymer valve leaflet for a prosthesis, said mandrel comprising a bodyportion including an outer surface having a plurality of ridges, and atleast one contoured surface between said plurality of ridges, wherebysaid at least one contoured surface corresponds to at least one leafletfor said prosthesis, said at least one contoured surface including anupper edge portion corresponding to the upper free edge of said at leastone leaflet, said mandrel further comprising a mandrel extension portiondisposed above said body portion, and an intermediate circumferentialgap extending around said mandrel between said upper edge portion ofsaid at least three contoured surfaces and said mandrel extensionportion.
 2. The mandrel of claim 1 for molding at least three polymerleaflets for a prosthesis, wherein said body portion includes an outersurface having at least three ridges and at least three contouredsurfaces between said at least three ridges corresponding to at leastthree leaflets for said prosthesis.
 3. The mandrel of claim 1 whereinsaid body portion comprises a substantially cylindrical body portion. 4.The mandrel of claim 1 wherein said circumferential gap includes a gaphaving a depth of between about 1 and 5 mm.
 5. The mandrel of claim 4wherein said circumferential gap has a depth of between about 1 and 2mm.
 6. The mandrel of claim 1 wherein said gap has a width between about0.5 and 5 mm.
 7. The mandrel of claim 6 wherein said gap has a width ofabout 1 mm.